1. Field of the Invention
The invention relates to an activation unit with at least one actuator having a variable length around at least one first axis, which operatively interacts directly or indirectly with an activation element mounted to be bi-directionally deflected along a second axis.
2. Description of the Prior Art
Activation units of the aforementioned kind are known in a wide variety of technical applications for path and/or pressure transfer in the form of stroke or force transmitting elements. Reference is made in this regard to DE 39 16 539 C2, describing an activation unit with two piezoceramic actuators, which are spaced apart relative to each other along a shared first axis, and are each subjected to a lengthwise expansion directed toward each when electrically activated. Each individual actuator activates a cylinder plunger, which becomes engaged with a pressure transfer medium disposed along the first axis symmetrically between both actuator cylinder plunger pairs. The cylinder plungers, which act bilaterally on the medium, cause an elastomeric material functioning as the pressure transfer medium to experience a bi-directionally guided compression along the first axis, as well as an elastic expansion along a second axis oriented orthogonally to the first axis. Along the second axis, the elastomeric pressure transfer medium comes into contact with an activation element which is a spacer bolt which is linearly deflected to trigger a technical function. Such an activation unit makes it possible to largely decouple mechanical oscillations between the activation element and piezoceramic actuators caused by the interconnected elastomeric pressure transfer medium such as for example those encountered in combustion engines. First and foremost, however, the pressure transfer medium as well as the cylinder plunger surfaces bordering the pressure transfer medium are used relative to the surface of the spacer bolt bordering the pressure transfer medium for purposes of an adjustment path and adjustment force transfer with respect to the actuator length changes initiated by the solid-state actuators. In order to increase the adjustment path and adjustment force, the selected bolt surface must be smaller than the cylindrical plunger surfaces.
Described in DE 197 05 893 A1 is a modular actuating and control unit for use in various hydraulic and pneumatic valves, which is powered by at least one solid-state actuator preferably designed as a stacking actuator, whose first actuator end is fixedly supported against a mechanical counter bearing, and whose freely movable second actuator end is joined with a first piston that unilaterally borders a hollow space inside a housing. The housing contains a transfer medium in the form of an incompressible liquid, such as water or hydraulic oil. Opposite the first piston in an axial direction of action, a second axially movable stamp unilaterally seals the hollow space impermeably to fluids, and when correspondingly activating the actuator, it is axially deflected by the transfer medium that transfers the force to an extent proportional to the area ratios of both piston surfaces directly bordering the transfer medium.
DE 102 03 659 A1 discloses a fuel injection valve having an adjustment path mechanism comparable to the actuating and control unit described above, with a stacking actuator connected with a first piston, which is in turn operatively connected with an encapsulated rheological liquid as the transfer medium. Likewise, a second axially deflectable piston borders the encapsulated rheological liquid, wherein the piston surfaces of both pistons which are operatively connected by way of the transfer medium, differ from each other making it possible to realize an adjustment path or adjustment force transfer from one to the other piston.
Instead of a rheological liquid as the transfer medium, the actuating or drive element described in DE 44 07 962 C1 provides an elastomer body as the transfer medium that is also bilaterally bordered by a first and second adjustment path piston, having a first piston is operatively connected with a solid-state stacking actuator and a second piston serving as a drive element for the actuator.
The known piezoelectrically powered activation elements for adjustment path and force transfer are used for a plurality of different applications, but preferably in adjustment valve systems used for control purposes in fluidics or pneumatics. However, as the time usage for which these types of activation elements increases, the properties of the activation units change with regard to the magnitude and dynamics of the achievable adjustment paths and adjustment forces alike. This phenomenon is typically not desired. Such changing properties may stem from different causes, which have to be examined so that adequate countermeasures can ultimately be taken, or operationally induced changes in the properties of such activation elements can be advantageously implemented in a technically usable manner depending on their operationally induced causes.